The invention relates to a process for the preparation of 1,2-dioximes of the general formula A--C(.dbd.NOH)--C(.dbd.NOR)--R wherein A represents an aromatic group and R a hydrocarbyl group or a hydrogen atom.
Vic-dioximes, including the 1,2-dioximes of the above formula, are widely known materials. Because of their recognized ability to form chelate complexes with certain metal ions, these dioximes have utility as reagents for use in the quantitative analysis of metals and as extraction agents in liquid/liquid extraction processes for the recovery of metals in the course of mining operations.
It is known that 1,2-dioximes of formula A--C(.dbd.NOH)--C(.dbd.NOH)--may be prepared from hydroxyiminoketones of the formula A--C(.dbd.O)--C(.dbd.NOH)--R or the formula A--C(.dbd.NOH)--C(.dbd.O)--R, wherein A and R are as heretofore defined, by reaction with hydroxylamine. Synthesis of vic-dioximes in this general manner is disclosed, for example, in Methoden der organishen Chemie, Houben-Weyl, Vol. X/4 (1968), p. 61-64, and by C. V. Banks in Record of Chemical Progress, Vol. 25, No. 2 (1964), p. 85.
Methoden der organishen Chemie further teaches, at pages 282-294 of Vol. X/4, that vic-dioximes exist in the anti, the syn, and two amphi configurations, which may be represented as follows: ##STR1##
It is generally known that these configurations exhibit different physical and chemical properties. In this regard, the commonly-assigned copending application having Ser. No. 016,679, filed Mar. 1, 1979, which is a continuation of application Ser. No. 884,054, filed Mar. 6, 1978, now abandoned, and the copending continuation thereof, Ser. No. 16,679, filed Mar. 1, 1979, disclose that the anti form of certain 1,2-dioximes out-performs the syn and amphi configurations when used as the active chelating agent in a liquid/liquid extraction process for the recovery of nickel from aqueous solution. Another commonly-assigned copending application, Ser. No. 884,337, filed Mar. 7, 1978, now U.S. Pat. No. 4,173,616, discloses that hydroxyoxime extractant mixtures comprising the anti configuration of various dioximes exhibit synergistic performance in accomplishing the extraction of copper, while mixtures comprising the syn and amphi configurations do not.
In view of recognition in the art of the advantageous properties of the anti isomer of 1,2-dioximes, a process for the preparation of 1,2-dioximes which maximizes production of the anti isomer and minimizes production of the syn and amphi isomers would be highly desirable. However, conventional preparation of a 1,2-dioxime by reaction of the corresponding hydroxyiminoketone with hydroxylamine has resulted in a product containing a relatively low proportion of the anti configuration.